Unnamed Brother: Not much is known about her relationship with her brother.
Terumi Minamoto: Kaoruko relationship with Terumi is borderline incestuous. Shamelessly stripping in front of him, making sexual innuendos, playfully touching his genitals and allowing him to fondle her breast. Despite her perverted nautre, she cares deeply for Terumi and maintains strong familial bonds with him. As she was instrumental in helping him get over his fear of woman and milk. And when he is crestfallen after a break, she will comfort him with the warm embrace of her bosom. She also let him stay at her home when he was evicted by his father after remarrying. However, she will use him to further her own research even it causes Terumi discomfort and embarrassment.